This invention relates to coil spring dampers and more particularly to helical coil spring dampers which operate to inhibit resonant oscillation of coil springs such as may occur in valve assemblies of internal combustion engines.
Helical coil springs have long been used to provide a biasing force for an object which must undergo reciprocal motion. Successful internal combustion engine designs have continuously featured helical coil springs to bias combustion chamber valves to a closed position. In a typical four cycle internal combustion engine for example, a combustion chamber valve is opened and closed once per two revolutions of the crankshaft. Thus, valve speed is directly proportional to engine speeds. At high engine speeds, valve springs have been known to resonate. Such resonance may result in erratic valve operation as well as possible damage to the engine and/or valve spring and in general impaired engine performance.
Various techniques have been used to eliminate valve resonance. One such technique is to increase the force and/or the constant of the helical coil spring. The disadvantage of this solution is that the required valve actuator force is increased, thereby increasing internal energy losses resulting in increased fuel consumption and increased valve train wear.
Another technique is to shroud the helical coil spring with a sleeve anchored by prong-like members between the helical coil spring and the spring seat. Such a construction is shown in related application Ser. No. 398,501, filed July 15, 1982, U.S. Pat. No. 4,479,461 entitled "Coil Spring Damper For Valve Assemblies Of Internal Combustion Engines And The Like". While this arrangement does effectively attenuate resonant oscillation of the coil spring, the edges of the radially extending prongs have a tendency to gouge or machine the spring seating surface of the cylinder head surrounding the valve stem. This machining action results from the inherent rotational movement of the valve spring and associated damper during repetitive actuation thereof. This wearing or machining of the valve spring seating surface may result in contamination of the lubrication oil with metal particles as well as possibly eventually result in reduction of the spring biasing force required for proper operation of the valve. This is of particular concern with head assemblies fabricated from aluminum alloys but is an undesirable condition in any application.
Accordingly, the present invention provides a coil spring damper assembly which overcomes the disadvantages associated with this prior construction by incorporating a continuous annular spring seat engaging surface on the axial end of the cylindrical damper sleeve thus eliminating the presence of any radially extending edges which may result in excessive wear of the seating surface. The cylindrical member is constructed to be mounted about the helical coil spring and to frictionally engage the outer periphery of a plurality of the helical coil spring coils. The cylinder when mounted about a portion of the helical coil spring exerts a radial resilience to dimensional variations in the helical coil spring during compression and expansion. Such engagement between the sleeve and portions of the helical coil spring dampens the helical coil spring motion thereby increasing the valve resonant frequency without significantly increasing internal engine power losses.
Additional objects, advantages and features of the present invention will become apparent from the subsequent detailed description of the preferred embodiments and appended claims taken in conjunction with the accompanying drawings.